The use of ophthalmic lenses for the correction of ametropia is well known. For example, multifocal lenses, such as progressive addition lenses (“PALs”), are used for the treatment of presbyopia. The progressive surface of a PAL provides far, intermediate, and near vision in a gradual, continuous progression of increasing dioptric power from far to near focus.
Any number of methods for designing and optimizing progressive surfaces are known. These methods are disadvantageous in that the lens performance is defined in terms of surface aberrations, namely surface astigmatism and mean power error, surface form, or both surface aberrations and form. Optimizing lens performance based upon surface calculations results in a lens that will not perform optimally in conjunction with the eye. Additionally, by limiting the surface shapes to a particular mathematical form, the optimum form of the design cannot be achieved. Still further, by optimizing the lens performance using surface aberrations, optimization of a PAL having more than one progressive addition surfaces requires optimization of each surface separately limiting the designer's ability to balance the aberration contributions from each of the surfaces to provide the best possible overall lens performance.